THIS IS A RUSH TRANSCRIPT. THIS COPY MAY NOT BE IN ITS FINAL FORM AND MAY BE UPDATED.

[18:00:01]

WOLF BLITZER, CNN ANCHOR: But some GOP lawmakers now saying they are open to meeting with him. Are there cracks in the Republican wall of opposition?

Bern out? President Obama reportedly telling donors at a private fund-raiser that Democrats will soon need to unite behind Hillary Clinton, but, tonight, the White House pushing back, saying the president didn't indicate a preference for Hillary Clinton or Bernie Sanders. Which candidate does President Obama want to see win the nomination?

And terrorist control, the U.S. military sharpening its focus right now on ISIS hideouts inside Iraq and Syria and doubling down on the number of Arab fighters willing to take on ISIS forces. Is the war against the terrorist nearing a turning point?

We want to welcome our viewers around the United States and around the world. I'm Wolf Blitzer. You're in THE SITUATION ROOM.

ANNOUNCER: This is CNN breaking news.

BLITZER: Dramatic developments tonight in the Republican race for the White House as details are emerging of a closed-door meeting of top conservatives determined to stop Donald Trump.

With a growing number of GOP officials openly talking of a contested convention, the group led by blogger and radio host Erick Erickson is now pinning its hopes on a convention fight that would allow a unity ticket to eventually win the nomination over Trump. The group is also leaving a door open to supporting a third party if Republicans are unable to stop Trump from becoming their nominee.

And there's breaking news in the Democratic race as well. The White House now pushing back against a "New York Times" report saying President Obama privately told donors the party will soon need to unite behind Hillary Clinton.

Tonight, a spokesman says the president does believe the party needs to come together around the eventual nominee, but did not specify Clinton or Bernie Sanders.

We're covering all of this, much more this hour with our guests, including senior Trump adviser Stephen Miller. Our correspondents and expert analysts, they are also standing by.

Let's begin with the Republican race. CNN's Sunlen Serfaty is in Houston for us with the latest.

Sunlen, the stop Trump movement within the party seems to be growing tonight. What's the latest?

SUNLEN SERFATY, CNN NATIONAL CORRESPONDENT: That's right, Wolf. It does appear to be picking up steam tonight among conservative Republicans.

Emerging from that meeting in Washington, D.C., that anti-Trump meeting was this call for potentially a unity ticket potentially between Kasich and Ted Cruz teaming up together, and, yes, the possibility of running a third-party candidate all in an effort to stop Donald Trump.

(BEGIN VIDEOTAPE)

DONALD TRUMP (R), PRESIDENTIAL CANDIDATE: We have to bring our party together.

SERFATY (voice-over): As Trump calls for unity, the stop Trump movement is huddling in Washington, D.C., today to do anything to stop him.

Sources tell CNN there was absolute consensus in the closed-door meeting on trying to stop Trump from getting the number of delegates needed to clinch the nomination, but that there was a real division about launching a third-party challenge if Trump ultimately becomes the nominee.

Tonight, Paul Ryan is brushing off the idea that he could be drawn in to the presidential race.

REP. PAUL RYAN (R-WI), SPEAKER OF THE HOUSE: It's not going to be me. It should be somebody running for president. People are out there campaigning.

SERFATY: But the House speaker is not stepping away from the prospect that his party might be heading towards a contested convention.

RYAN: This is more likely to become an open convention than we thought before. So we're getting our minds around the idea that this could very well become a reality.

SERFATY: Trump's team encouraging Republicans opposed to Trump to rethink their strategy.

BARRY BENNETT, TRUMP CAMPAIGN SENIOR ADVISER: When we get to Cleveland, he's going to be our nominee. And, you know, some of these guys are going to have to decide how much damage they're willing to do to the party because they don't like that.

SERFATY: Marco Rubio, meantime, is back on Capitol Hill speaking for the first time today since announcing his departure from the race, but not letting up on the GOP front-runner.

SEN. MARCO RUBIO (R), FLORIDA: Hopefully there's time to still prevent a Trump nomination, which I think would fracture the party and be damaging to the conservative movement.

SERFATY: And avoiding questions about a possible endorsement.

RUBIO: I don't have any announcement today.

SERFATY: The potential for a contested convention is now pushing the GOP candidates into effectively waging two campaigns side by side, still working to win outright, but also scrambling to prepare their backup plans if the nominating fight is still unsettled before Republicans gather in Cleveland this July.

SEN. TED CRUZ (R-TX), PRESIDENTIAL CANDIDATE: Look, if Donald and I come in and we're neck and neck and neither of us are at 1,237, then it's a battle for the remaining delegates. Then that's actually how a convention operates.

GOV. JOHN KASICH (R-OH), PRESIDENTIAL CANDIDATE: It is unlikely that anybody is going to achieve enough delegates to avoid a convention.

SERFATY: The campaigns are also closely watching the delegate math.

Candidates need to get to 1,237 delegates to clinch the nomination before the convention. Based on the current delegate counts, Donald Trump would need to win a little more than 50 percent of the remaining delegates to reach that mark.

[18:05:08]

Ted Cruz would need roughly 80 percent. And for John Kasich, it would be mathematically impossible. He would need about 108 percent.

South Carolina Senator Lindsey Graham today telling CNN's Dana Bash that he sees Cruz as the best hope for stopping Trump.

SEN. LINDSEY GRAHAM (R), SOUTH CAROLINA: I think the best alternative to Donald Trump, to stop him from getting to 1,237, is Ted Cruz. And I'm going to help Ted in every way I can.

(END VIDEOTAPE)

SERFATY: And Lindsey Graham will work to raise money for Senator Cruz now. He will be headlining a fund-raiser for him in Washington, D.C., on Monday, fund-raising now even more essential given this prospect of this extended primary -- Wolf.

Another major political battle unfolding tonight, President Obama's nomination of Judge Merrick Garland to the U.S. Supreme Court. Senate Republicans are still ruling out a confirmation hearing, but some, including the chairman of the Judiciary Committee, are now saying they're at least willing to meet with Judge Garland.

Our justice correspondent, Pamela Brown, has more.

Pamela, Judge Garland has been up on Capitol Hill today. How did that go?

PAMELA BROWN, CNN JUSTICE CORRESPONDENT: Yes, it's been a very busy day for Judge Garland. He met with Democratic senators.

And as this was happening, some Republicans softened their positions, and they say they are considering at least meeting in private with the president's nominee.

(BEGIN VIDEOTAPE)

BROWN (voice-over): Senate Minority Leader Harry Reid and President Obama's new Supreme Court nominee, Merrick Garland, met privately today, with Reid vowing he won't back down in the face of fierce opposition.

SEN. HARRY REID (D-NV), MINORITY LEADER: The concern that we have, especially after meeting this good man, is why can't the Republicans just do what they are supposed to do, do their jobs?

BROWN: Republican leaders in the Senate are refusing to budge on giving Judge Garland a hearing, saying it's not about the person. It's about the principle of not confirming a nominee in a presidential election year. But there are subtle cracks in the GOP blockade.

While Majority Leader Mitch McConnell says he won't even sit down with Garland, a handful of Republicans are open to meeting with him, including some who are up for reelection, like Judiciary Committee Chairman Chuck Grassley.

SEN. CHARLES GRASSLEY (R), IOWA: If I can meet with a dictator in Uganda, I can surely meet with a decent person in America.

BROWN: Senator McConnell writes in an op-ed in "USA Today": "The American people deserve a voice in such a momentous decision."

But President Obama says the voters did have a voice when they elected him. On a phone call with supporters today, he said -- quote -- "They didn't add a caveat that said we want you to be president except for your last 300 days in office, when you don't have to fulfill your duties."

On the steps of the Supreme Court, Democrats contend Republicans are putting politics above the law.

SEN. CHARLES SCHUMER (D), NEW YORK: Judge Garland is a widely respected legal mind who puts the law above ideology, exactly the type of nominee that Republicans profess to love when it comes to the Supreme Court. You simply can't lay a glove on him.

(END VIDEOTAPE) BROWN: And Democrats are holding out hope that with Republicans going back home for recess today, they will face public opposition to their vow of not giving a hearing and change course.

Meantime, Wolf, Republican leaders today ruled out confirming Garland in the lame-duck if a Democrat is elected president.

BLITZER: Pamela, thanks very much -- Pamela Brown reporting for us.

Let's get some more on all of this, including the race for the White House.

Senior Trump adviser Stephen Miller is here. He was a top aide to Senator Sessions until recently.

Now you're working with the Trump campaign. Right?

STEPHEN MILLER, SENIOR TRUMP CAMPAIGN ADVISER: That's right.

BLITZER: Do you think he can get enough votes, 1,237, that's the number you need, to get the nomination outright on the day he arrives there in Cleveland in July?

MILLER: We're feeling very confident about it right now, Wolf.

And we had a great night. We obviously had a huge victory in Florida, winning the biggest prize of the night and winning every single county in the state but one. And now we're heading into a part of the race where it's going to be very favorable for Mr. Trump, huge delegate states like New Jersey, New York, California.

We expect we're going to get what we need to get to 1,237.

BLITZER: What do you think of these conservatives, though, these faith conservatives, meeting here today, establishment conservatives? They are meeting. They're looking for a way to prevent Donald Trump from getting that nomination. They are hoping for some sort of contested convention in which somebody else would emerge.

MILLER: I think the most important thing to keep in mind is that they aren't just trying to deny the nomination to Donald Trump.

What they are truth to do is deny tens of millions of patriotic Americans control over their own economic futures. They are worried that the gravy train is going to shut down if Donald Trump is the nominee. That's what this is all about.

BLITZER: What do you mean by the gravy train?

MILLER: So, as you mentioned, I worked for Jeff Sessions, one of the most honorable men in Washington. But I had...

BLITZER: Who supports Trump.

MILLER: Who supports Trump. And I had an up-close seat to the corruption in Washington, D.C., and

I saw firsthand -- and I will give you a good example. One of the groups opposing Mr. Trump is the Club for Growth.

[18:10:08]

In 2011, we were pushing a bill to stop Chinese currency cheating. The Club for Growth fought against us to preserve offshoring of jobs to China. What you have is groups that make a killing off of bad trade deals, bad immigration bills that are trying to keep Trump out of the White House because he's going to cost them and their corporate clients money.

Make no mistake. All of the groups arrayed against Trump, their motivation is selfish economic interest.

BLITZER: But how much of a threat does it represent to Donald Trump?

MILLER: I don't think it does. One of the names you mentioned today was Erick Erickson. To be candid, most people watching today are thinking, who is Erick Erickson? Really, who is Erick Erickson?

BLITZER: He's a popular blogger, a radio talk show host. Used to be a contributor here on CNN. I think he's a contributor now to FOX.

MILLER: But the point is, is that Erick Erickson doesn't have control over who the GOP nominates. Erick Erickson doesn't get to decide who the future of the Republican Party is.

The reality is that the average Republican voter has been killed by offshoring of jobs, by an open border, by a terrible foreign policy that has enmeshed us in all kinds of disastrous foreign conflicts. And they're saying, please give us relief from these terrible policies.

BLITZER: If there -- there are even some threats out there that he does get the nomination, a third-party candidate could emerge in a general election. So it would be Donald Trump, let's say the Republican nominee, let's say Hillary Clinton the Democratic nominee, a third-party conservative would emerge.

That presumably would only help Hillary Clinton get elected president of the United States.

MILLER: Right.

What you see in this desperation is people are terrified that they are losing control of a party they once ran. And these people, again, I worked with them for many years. They are used to calling the shots. And, frankly, they're mad that instead of being able to issue orders from their fancy lobbying firms in D.C., you know who is going to be in charge under a Trump administration?

The steel worker, the guy who goes to work every day for $12, $15 an hour. That's who is in charge, not the person with a $2 million salary lobbying in Washington, D.C. BLITZER: If he is shut out of the nomination at the convention, do

you think he would, Donald Trump, as a third-party candidate himself?

MILLER: Well, Donald Trump has said that he is going to run as the Republican nominee. And he's been clear on that point.

And, again, we're on path to get 1,237 delegates. And I just think it's critical that people understand the stop Trump movement is about one thing only. It's about people trying to retain their own power.

BLITZER: Stand by. We have a lot more with Stephen Miller coming up. We will get your reaction to what the speaker of the House is now saying, among other new developments. We will take a quick break. We will be right back.

(COMMERCIAL BREAK)

[18:17:05]

BLITZER: Top Republicans now talking openly of a contested convention, as panic seems to develop over a possible Donald Trump nomination.

Top conservatives meeting in Washington today are hoping a unity ticket will defeat Trump in multiple convention ballots. But the group did leave the door open to potentially supporting a third-party ticket if Republicans are unable to stop Donald Trump.

We're back with senior Trump adviser Stephen Miller.

Paul Ryan is saying a contested convention, his words -- he's the speaker of the House -- is more likely. You agree? You think that's true?

MILLER: I don't agree.

And people can speculate whether they think it's more likely or less likely. But we think we're on path to get 1, 237.

BLITZER: You're pretty confident about that?

MILLER: Yes, we are.

BLITZER: You heard Sean Spicer, the chief strategist and communications director for the Republican National Committee, told me -- he told me last hour that the leadership, they basically show up in Cleveland a week before, and they can come up with new rules for the convention, change the rules, if you will, as they did in 2008, 2012.

I assume that's OK with you?

MILLER: I think what would be the right thing to do would be for the Republican Party to embrace the chance to grow. The GOP has been shrinking for years. And, again, I have been here in Washington for 10 years. And we keep shrinking and shrinking and shrinking.

A great example of why we have been shrinking is because we're pushing away blue-collar voters.

It would be insane to try and deny Trump the nomination. To even make the effort would be insane, because we're growing the party. We're going to win in Pennsylvania. We're going to win in Ohio. We're going to win in Florida. We're going to win in New York.

We're building a bigger Republican Party by reaching out to the blue- collar voters who have been turned away from both parties and bringing them into our tent.

DONALD TRUMP (R), PRESIDENTIAL CANDIDATE: If we're at 1,100 and somebody else is at 500 or 400, because we're way ahead of everybody, I don't think you can say that we don't get it automatically. I think it would be -- I think you would have riots. I think you would have riots.

You know, I'm representing a tremendous, many, many millions of people.

(END VIDEO CLIP)

BLITZER: Do you think he regret using the word riots?

MILLER: I think he was speaking figuratively.

And the media, everyone understands that he was speaking figuratively. But I think I really do want to underscore for you and for everyone else that you used the word earlier panic. Who is panicked, and why are they panicked?

The rich and powerful are panicked because they are losing control of the GOP. It's being returned to the voters.

BLITZER: Senator Lindsey Graham, he was once running for president, didn't exactly work out for him. He told our Dana Bash today he's now supporting Ted Cruz.

He's going to have a fund-raiser for him, I think, on Monday. He said the Trump campaign's campaign is built on xenophobia, race-baiting and religious bigotry. What's the Trump campaign's reaction to Senator Lindsey Graham?

[18:20:00]

MILLER: If Lindsey Graham would write a book, it could be called, how to shrink the Republican Party by Lindsey Graham.

Lindsey Graham is quite literally the expert in shrinking the Republican Party. Frankly, I wonder if Ted Cruz is going to reject the endorsement. Lindsey Graham is the one who came up with the foreign policy that's been such a disaster for the GOP.

Lindsey Graham is the one who came up with the immigration policy that's basically hollowed out the middle class. Lindsey Graham is a great person if you want to learn how to make the Republican Party smaller and less appealing to blue-collar voters.

BLITZER: Let me play for you -- this is a video from the pro-Hillary Clinton super PAC Priorities USA. They put out a response to a Trump video which we showed earlier. Let me play this little clip.

(BEGIN VIDEO CLIP)

UNIDENTIFIED FEMALE: Who are you consulting with consistently so that you're ready on day one?

TRUMP: I'm speaking with myself, number one, because I have a very good brain, and I have said a lot of things.

(LAUGHTER)

(END VIDEO CLIP)

BLITZER: There was a funny one yesterday with Hillary Clinton barking like a dog. That was the Trump ad. This is an anti-Trump ad. Your reaction?

MILLER: Well, I think Hillary Clinton comes off very poorly in the ad. I'm not really sure. Did her campaign actually make that ad?

BLITZER: No, it was a super PAC who supports her. She has nothing to do with it. But it's a pro-Hillary Clinton super PAC.

MILLER: OK. OK. Yes. That's right. Right.

The super PAC did a very bad job with the ad, because it ends with that clip of a very natural, affected moment from the candidate. So, I think that's just strange, just from like a professional standards point of view.

But Donald Trump is going to have a huge election against Hillary Clinton,because the issues the Democrats depend upon, Donald Trump is going to control, like the trade issue. He's going to hammer Clinton on her support for the TPP, the Trans-Pacific Partnership. And we're going to bring in the blue-collar voters. And she's going to end up having a very hard time connecting with them. BLITZER: Looks like Hillary Clinton is now spending a lot more time focusing in on a possible run against Donald Trump. Is the Trump campaign now spending more time focusing in on a possible run against Hillary Clinton, forgetting about the other Republican challengers, at least somewhat?

MILLER: Well, job number one right now is to go ahead and get 1,237. And that's where we're focused.

But you saw with our own ad that we're giving a little sampling, a little appetizer of how we're going to go after Hillary Clinton in the general election.

And, again, it's going to be a huge contrast on issues like trade and immigration, where we're going to side with working people and Hillary Clinton is going to side with big business and corporations.

And with Lindsey Graham endorsing Ted Cruz, that's really a remarkable development because it means that the people who favor offshoring, who favor foreign policy interventionism and who favor a failed legacy on trade are lining up behind Ted Cruz because they don't want anything in Washington to change.

BLITZER: Stephen Miller of the Trump campaign, thanks very much for joining us.

MILLER: Thank you.

BLITZER: Just ahead, we will have more on the effort by some leading conservatives to stop Donald Trump from becoming the Republican presidential nominee. Can they succeed where the party so far has failed?

Plus, Hillary Clinton and her supporters increasingly setting their sights on Donald Trump. How effective will their latest campaign ad be?

(COMMERCIAL BREAK)

[18:27:45]

BLITZER: Breaking news tonight: a new uprising against Donald Trump.

Top conservatives meeting today to plan a contested convention, hoping to deny Trump the nomination by putting forward what they call a unity ticket. And barring that, the group is also leaving the door open to backing a third-party ticket against Donald Trump, should he become the Republican presidential nominee.

SEN. LINDSEY GRAHAM (R), SOUTH CAROLINA: Well, I said if Trump or Cruz in the general election, I said, well, it's like being shot or poisoned. You're probably going to die anyway.

I would say this. Given Hillary Clinton's problems -- and they are mounting by the day -- that I think a Ted Cruz has a much better chance of beating Hillary Clinton than Mr. Trump.

I think Mr. Trump is trying to create division in the country that will not sell.

(END VIDEO CLIP)

BLITZER: All right, so, Dana, his decision, which must have been a painful decision for him based on everything he said until now, what does it say about the state of the Republican Party?

BASH: Well, as I said to him separately, I felt like I was going to, at that moments ago, see pigs flying down the street because I couldn't believe I was hearing Lindsey Graham, who has been very openly against and disdainful really of Ted Cruz, not so much personally, but his tactics in the Senate, saying that he thinks he's the best conservative right now, the most likely conservative to win, maybe not the best, but the most likely to win.

And that poison question, that was -- he was comparing Ted Cruz to Donald Trump. It wasn't that long ago saying that it's basically pick your poison. So, it means that they think that the best way to stop Trump, not necessarily get Ted Cruz enough delegates before the convention to be the nominee, but stop Trump from doing so, is to back Ted Cruz, because he's in second place when it comes to the delegates.

BLITZER: Nia, they're also talking, if they can't stop Donald Trump, he gets the Republican nomination, of a third-party ticket, which presumably would split the Republican vote and ensure that Hillary Clinton -- let's say she's the Democratic nominee -- wins the presidency.

[18:30:06] HENDERSON: It's hard to see a situation different than that where the third party doesn't play a spoiler role and Hillary Clinton is the beneficiary.

But also, I think the other alternative with Trump being the nominee, that's also probably a bad choice for the Republican Party. It would alienate a whole swath of voters, particularly suburban white women, so that's a problem. I think we are seeing, essentially, two parties here. We're seeing

one that's led by Trump and one that is the anti-Trump wing that doesn't really have a leader at this point.

I was texting with one Republican. And I said, you know, "What's going to happen with your party?"

And he said, "Well, maybe it just needs to burn to the ground to be reborn." And in some ways it feels like -- yes, I mean, and that's what it feels like if you have a convention, imagine the kind of upheaval that comes out of that convention if they try to bring somebody else in, if they -- if they steal the nomination from Donald Trump. So a lot of troubled waters ahead, I think, for this party.

BLITZER: Ron, you wrote an article about the future of the Republican Party. Rests with Donald Trump, you say. Is it too late right now for the Republicans to stop Donald Trump, or is there math that makes that possible?

BROWNSTEIN: Well, I think there's a difference between what's mathematically possible and what's politically practical. It is totally plausible that he will get to Cleveland without the 1,237 that he needs. I think it is not plausible that anybody else is going to get there with nearly as many delegates as he has.

If you look so far, Wolf, he has had a much bigger, broader coalition than any of his rivals. Ted Cruz is too dependent on evangelical Christians. He's not been competitive among voters who are not evangelicals. John Kasich is confined to moderates. So I think Donald Trump is -- has the strongest position; yet he's only at 38 percent, 37 percent of the total vote so far, and you are seeing this digging in against him.

We talked about this before. If anybody else had won the kind of states he's won in the last few weeks we'd be seeing the party talking about consolidating behind him. But for a variety of reasons, including the threats of him as a general election nominee, you're seeing the opposite.

So I think it is -- as Nia said, it is very troubled waters ahead. And either way they go -- either they nominate Trump and they have a fracture or they deny him the nomination and they likely have a fracture -- Republicans are facing a difficult set of choices in the weeks ahead.

BLITZER: How do you see this, Ryan?

LIZZA: I think that's a good point, is that it is a hardening of both sides. Right? The pro-Trump faction is more behind him than ever, sees the kind of things we're talking about -- a third-party run or denying him the nomination at the convention -- as a sort of conspiracy of the Washington elites, the same thing that Trump has been running against.

I think what Nia said is exactly right. This division in the party is between traditional conservatives, despite the debates that someone like Ted Cruz and Lindsey Graham has between them on foreign policy, you know, on a whole array of issues. They are more closely aligned about what it means to be a Republican than Donald Trump.

And so even Lindsey Graham would rather have someone like Ted Cruz. I think Lindsey Graham personally dislikes Ted Cruz. It's not just ideological differences there. But he'd rather have Ted Cruz as the nominee than Donald Trump, who would turn the party on foreign policy into something totally different. On trade, something totally different. More it more ethno-nationalist, frankly, and make it into a party that would alienate a lot of non-white voters. And that's the two visions they're looking at.

BASH: It is two visions, but it really is stunning that the people who were at this meeting today here in Washington, the conservative activists led by Erick Erickson, who's the founder of Red State, an influential conservative blog. He was one of the early Republican or sort of conservative Republican kind of disruptors, you know, making it tough for the establishment Republicans here in Washington.

LIZZA: Yes.

BASH: And now he finds himself on the same side as them, because that kind of anger and that kind of push to shake things up here has gotten...

HENDERSON: Too far.

BASH: Too far.

HENDERSON: Towards Trump, exactly.

And it really has, I think, solidified those blue-collar white workers who believe kind of a mix of things, whether it's about trade. Even some I talked to are for single-payer health care. I mean, it's a real mix. There's no Republican orthodoxy that the Republican Party has used typically to attract these voters. I mean, all of that checklist is just really out the window.

BLITZER: Ryan, you wanted to weigh in?

BROWNSTEIN: Real quick, I mean, that is an important point. Trump is engineering an historic shift of power in the party. I mean, he is -- you know, the heart of his coalition are these working-class white voters. He's won most of them in 17 of the 20 states with exit polls. He's only won most college-plus voters in 8 of the 20 states with exit polls. And their priority -- those working-class white voters are about half of the Republican electorate -- are very different than the national leadership of the party. They support entitlement programs for the elderly. They oppose free trade. They are deeply hostile to immigration and, in any case, to the cultural and demographic diversity of the country.

So what we are seeing is a shift in the balance of power in the party; and the reaction to that is the backlash that you are seeing against Trump on the other side. BLITZER: Dana, today we heard from Senator Marco Rubio, who was back

in the Senate doing his job. He said he met with reporters. He's not going to run for the Senate again. He's not -- he's going to give up his seat at the end of the year. He's not going to run for governor, he says, of Florida. He doesn't want to be vice president of the United States. He wants to become a private citizen.

[18:35:16] What happens to his delegates? Those 130, 140, 150 delegates that are pledged to him? There are 171 actually. There you see it right there, 171. That could be pretty critical.

BASH: It could be critical. I'm going to say that on the Senate, before I move on to the delegates, he had to choose, by law in Florida, whether he was going to run for president, be on the ballot for president or for Senate. By party rules down there. And that's why he chose the presidency and decided not to run for re-election.

Now, on the delegates, it's a complicated answer, because it's basically a state by state rule as to whether or not, when a candidate suspends his campaign, whether or not those delegates in that state are freed up or whether or not he can still have control over them; and different states, again, have different rules on that.

But the bottom line is he personally can't come to the convention -- let's just say there's an open convention -- and say, "My 171 delegates, I want you all to go to Ted Cruz." It doesn't work that way.

BLITZER: All right, guys. Stand by. We're going to take a quick break. We're just getting some breaking news, in fact, on the Democratic side. What's going on between Bernie Sanders and Hillary Clinton? We'll share that with you right after this quick break.

(COMMERCIAL BREAK)

ANNOUNCER: This is CNN breaking news.

[18:41:10] BLITZER: And we're getting in the breaking news right now. We're finally able to report that Hillary Clinton is the winner of the Missouri primary. She finished 1,531 votes ahead of Senator Bernie Sanders, who now says he will not contest the vote count in Missouri.

All this comes as the White House is now denying a "New York Times" report that President Obama is urging Democrats to unite behind Hillary Clinton.

Our senior Washington correspondent, Jeff Zeleny, is joining us now with new details. What are you learning, Jeff?

JEFF ZELENY, CNN SENIOR WASHINGTON CORRESPONDENT: Well, Wolf, with this Missouri win, the sound from Democrats is even increasing that it's time for this primary fight to wrap up. But you won't hear Hillary Clinton herself calling on Bernie Sanders to drop out. She needs his voters. Some 6 million have already supported him in the primaries so far. That number is only going to grow.

But some Democrats aren't waiting to start taking on Trump.

(BEGIN VIDEOTAPE)

ZELENY (voice-over): Donald Trump was one of the best Democratic punchlines around.

HILLARY CLINTON (D), PRESIDENTIAL CANDIDATE: He's making the most out of it. I'm having a good time watching it. I find it...

ZELENY: The Democratic Party is no longer laughing. As the primary fight between Hillary Clinton and Bernie Sanders goes on, "The New York Times" is reporting President Obama told donors in Texas last week it's time for Democrats to rally behind Clinton, an assertion the White House denied today. But there's little question the party is quickly turning its focus to Trump.

CLINTON: Our commander in chief has to be able to defend our country, not embarrass it.

ZELENY: Liberal groups are sounding the alarm, suddenly taking Trump seriously as a general election foe. From labor unions to environmental groups, the Democratic machine is spinning into action, trying to do what the Republican establishment could not.

SEN. HARRY REID (D-NV), MINORITY LEADER: Most of us cannot fathom how he rose so far and so, so fast. His vile rhetoric is embarrassing. His proposals are dangerous.

ZELENY: Nearly two dozen progressive groups signed a letter this week saying it's time to unite. They're calling this moment "a five-alarm fire for our democracy."

One day after Trump released this video making fun of Clinton...

CLINTON: (BARKING)

ZELENY: ... the Clinton super PAC returned fire by using Trump's own words against him.

UNIDENTIFIED FEMALE: Who are you consulting with consistently so that you're ready on day one?

DONALD TRUMP (R), PRESIDENTIAL CANDIDATE: I'm speaking with myself.

ZELENY: But Clinton hasn't won the nomination just yet. Sanders is trailing in delegates, but he's far from folding. But Clinton is running a dual track strategy, keeping one eye on Sanders and another on Trump.

CLINTON: I've gotten more votes than he has. I think he has, if you really analyze it, a pretty narrow base. But we'll find out. If he gets nominated, we're going to have a very vigorous general election if I'm the nominee.

(END VIDEOTAPE)

ZELENY: But that vigorous general election isn't here just yet. Sanders believes he'll win several of the next contests, starting with Arizona next week, followed by Washington state. But even so, Wolf, some Democrats are growing impatient and are beginning to invest time and money into defining Trump early, something they believe Republicans failed to do.

BLITZER: Jeff Zeleny, thanks very much.

Let's get back to our political experts for some more analysis. What does it say to you, Nia, that the president of the United States, White House pushing back on this notion he's effectively saying rally around Hillary Clinton? But he did say, the White House is saying that the president believes the party should come together behind a nominee. Talking like that to a bunch of political donors, what does that say to you?

HENDERSON: You know, I think this "New York Times" story, which they push back on, it really underscores what we've known for a while, which is that Barack Obama, President Obama does have a dog in the fight, and it's Hillary Clinton.

[18:45:03] His aide Jay Carney, his former aide, was on our air in February, essentially saying that Hillary Clinton is President Obama's choice. So, it's not a surprise.

But I think it also reflects a larger conversation and push in the Democratic Party. Let's wrap this up. Let's move forward and turn to the general election.

WOLF BLITZER, CNN ANCHOR: But for -- Ryan, for Bernie Sanders, a lot of us know him. It's not just getting the Democratic nomination, which he clearly wants. It's also getting his message out.

He's 74 years old. He's very passionate about these issues. If he walks away now that message is not going to get out the way he wants it to get out.

RYAN LIZZA, CNN POLITICAL COMMENTATOR: Absolutely right. There's a view in that wing of the party and in the Sanders campaign that to keep Hillary Clinton sort of on the right path, to keep her on the left, she needs political pressure all the time. This is the theory that Elizabeth Warren applies when she's trying to get something out of either the White House or Hillary Clinton, and this is theory of the Sanders campaign.

So, even as his campaign transitions less into something about winning the nomination, which is very unlikely he'll do, and more into a message campaign: one, he's well-funded. Two, he's going to have a lot of delegates if he goes all the way through to June 7th in California. He's going to show up in that conference with a lot of delegates and he's going to have more influence in the party if he can show that's it's an historic run based on votes and delegates.

DANA BASH, CNN CHIEF POLITICAL CORRESPONDENT: And the Bernie Sanders campaign and all of his supporters, they're not wrong. They have been able to pull Hillary Clinton to the left. They have been able to play a lot of this Democratic conversation on their turf --

LIZZA: Yes.

BASH: -- which never -- I mean, nobody ever thought was going to be able to happen which is kind of amazing for them. The good news for Hillary Clinton is that this is kind of where the political spectrum meets in the middle. When I say this, I mean Donald Trump and Bernie Sanders on some of the issues that Hillary Clinton has gone left on, like trade, for example.

If Donald Trump is her opponent, it won't hurt her that much to be anti-trade against a Republican. Traditionally Republicans are free trade. Not Donald Trump.

BLITZER: You know, Ron, you've studied these numbers about as close as anyone. Who would come out on top presumably in a general election between Donald Trump and Hillary Clinton? Because he says he would expand the Republican Party. He would put in play states like his home state of New York, for example, or Michigan, New Jersey, Pennsylvania.

For a Republican, that would be huge.

RON BROWNSTEIN, CNN SENIOR POLITICAL ANALYST: Yes, luckily, we get eight months to actually watch this play out.

But I think looking at the primaries, you have to say a couple of things. Donald Trump has shown the ability to master modern communication. He's dominated the news cycle in a way that we have not seen any other candidate do.

He's also shown the ability to connect tremendously with blue collar voters. That is the core of his support in the Republican Party. He's dominating among those voters. The single biggest reason he's the front-runner at this point.

But the structure he's built around this campaign does create demographic headwinds for the general election, because those blue collar voters he's relying on in the Republican primary, they have declined as a share of the electorate in every election since 1980, except one. Just since 2000 their share of the total vote has declined by 10 points, the cost of some of the very polarizing positions he's taken that have helped him with those voters is he has astronomical negatives among the groups that are actually growing as a share of the electorate -- millennials, minorities, college educated white women. He's looking at unfavorables in the 70 to 80 percent range of those with those groups, and they will all be a bigger share of the vote in 2016 than they were in 2012.

So, yes, there may be a path for Donald Trump, but it is a narrow one unless he can undo some of the damage that he's done during this primary season with the growing groups in the electorate.

BLITZER: But given, Dana, his unconventional campaigning, shall we call it, the thought is he could presume -- if he's running against Hillary Clinton, throw her off base.

BASH: Yes, and then some.

I was talking to a Clinton aide about this very thing this week. And the point being that, you know, look, she's a good candidate. I mean, she just is. She's gotten better and better as the weeks and months have gone forward here.

But what she's fighting with Bernie Sanders is conventional war. I mean, this is going to be the most unconventional political war we have ever seen. We've already seen it on the Republican side. But that's probably going to look like baby stuff compared to what we would see in a Clinton --

BLITZER: You agree, Nia?

HENDERSON: Yes, we've seen already that with him bringing up stuff about her husband, for instance. That's something that we hadn't really seen from other candidates who faced Hillary Clinton and now, the Republicans. So, this -- you know, it's almost like the Looney Tunes character, the Tasmanian devil on fire. I mean, that is how he is going to run, you know, run an election, just very unpredictable. He's a master of social media. He's a master of media in general. That's something that I think the Hillary Clinton campaign is going have to adapt to.

BLITZER: He'll be tweeting a lot.

HENDERSON: Yes.

BLITZER: He already does.

All right. Guys, thanks very much. Don't go too far away, as I say.

Just ahead, there's other breaking news we're following -- this time out of North Korea. U.S. officials have just confirmed that Kim Jong- un's regime has launched a ballistic missile.

[18:50:04] We're gathering new details. We'll have more right after the quick break.

(COMMERCIAL BREAK)

BLITZER: Breaking news: U.S. officials have just confirmed that North Korea has launched a ballistic missile off the east coast of the Korean peninsula. Our national security team is following the late breaking development.

Jim, what are you learning? JIM SCIUTTO, CNN CHIEF NATIONAL SECURITY CORRESPONDENT: We're learning now, U.S. intelligence officials and the military confirming that the North Korea fired a medium range Nodong missile 500 miles into the Sea of Japan. This, of course, into the east, to the direction of Japan, threatening both Japan and South Korea.

[18:55:02] The latest in a series of provocations by North Korea, including what is essentially an ICBM launch, their space launch earlier this year, as well as more recently, just two weeks ago short- range missile launches into the ocean off the coast of North Korea.

BLITZER: Let me bring in our Pentagon correspondent Barbara Starr.

What are you learning over there, Barbara?

BARBARA STARR, CNN PENTAGON CORRESPONDENT: Well, Wolf, U.S. officials have been watching the signs of a possible launch in the last couple of days. What is so interesting about this is this missile was launched off a mobile launcher, essentially a huge truck that can rol up and down the roads of the countryside of North Korea, very difficult for U.S. spy satellites to track.

It means that the North Koreans can launch off a mobile launcher with little or no warning to U.S. intelligence. They have done that before.

But right now, it is considered by U.S. military officials a sign, if you will, of additional North Korean provocation, perhaps sending a message to the U.S. we can do this. Don't forget. We know how to do this.

At the same time U.S. intelligence officials, U.S. military officials tell me they have been watching for signs that North Korea, in fact, even as they did this, maybe preparing for yet again another nuclear underground test -- Wolf.

BLITZER: All right. Our global affairs correspondent Elise Labott is also checking in with her sources.

Elise, what are you learning?

ELISE LABOTT, CNN GLOBAL AFFAIRS CORRESPONDENT: Well, Wolf, I just spoke with a senior U.S. official just a few minutes before coming onto the set. The official said, listen, none of these provocations that North Korea is doing are good, but this was an intermediate range missile that 800 kilometers or so, it did go into the sea.

So, the U.S. doesn't want to make a big reaction of it. I want to say it's not a big deal because each one of these tests that North Korea does definitely gives the North Koreans more knowledge for their long- range missile tests and more knowledge for their nuclear program.

And so, while the U.S. isn't concerned about any one provocation right now, they are worried that North Korea is going for the ultimate and what is that? A long-range intercontinental ballistic missile with -- that can fit a nuclear warhead on a missile and deliver it to the United States.

BLITZER: Do they have that miniaturized nuclear warhead capability?

SCIUTTO: Well, the fact is the U.S. intelligence say they do not know for sure, but they have to assume that that's possible. What they do say is North Korea has not successfully tested that capability, but they are making progress every day.

A space launch is effectively an ICBM. A mobile launcher makes it much more difficult for U.S. intelligence to track these launchers, and the assumption is that they're making progress towards miniaturizing. None of this is good news.

BLITZER: The timing of this, Barbara Starr, is significant. The U.S. and South Korean allies that have been engaged in these massive annual war games, if you will, these training exercises, the North Koreans do this. And every time the U.S. and South Korea, they do it, the North Koreans try to do something, right?

STARR: Well, that's right. It's what the Pentagon likes to call a provocation cycle by North Korea in the Pentagon's words. So, we're in a provocation cycle. North Korea making all these threats about a nuclear attack, about a missile attack.

They want to send a message -- launching a mobile missile does that because they know that the U.S. can't really track it as well as it wants to be able to, so they send that message. But -- and this is really very interesting. They picked a missile tonight that they knew would likely work.

This is an existing missile in their inventory. They are working on two additional mobile missiles that they haven't tested yet. The U.S. did not think they would use those untested missiles because Kim Jong- un would not want to be embarrassed in front of the world if those missiles did not work tonight, tomorrow morning obviously in North Korea right now.

So, he went the safe route. He picked a missile he knew would work, but he picked a mobile missile, knowing that he's sending a message to the U.S. military, I can do this. You may not be able to track what I'm doing exactly -- Wolf.

BLITZER: Not just a message to the U.S. military, it's a message to South Korea, to China, to Japan and others. Very quickly, it comes also after the North Koreans have sentenced a young American, a 21- year-old University of Virginia student, Elise, what, 15 years of hard labor for ripping off a propaganda poster. That's another message that the North Koreans are sending.

LABOTT: It's another message all around that the U.S. is not basically in the driver's seat here. You have a former ambassador, Bill Richardson, who is working on trying to get his release, but certainly this complicates matters with the United States. The U.S. doesn't have a real hand and is unfortunately going to have to give some concessions to get rid of this gentleman. But right now -- to get this gentleman back. But right now the concern for the U.S. is these provocations. Will it

come out of control? And the U.S. will not be able to stop some kind of miscalculation?

BLITZER: Let's not forget, the U.S. still has about 28,000 troops, ground troops, along the demilitarized zone, separating North and South Korea. So, the U.S. has a huge stake involved over there.

All right, guys. Thanks very much. We're going to stay on top of the breaking news. Stay with CNN for more information.